Large capacitance varicaps, where are thee?

Because you refuse to consider any other supplier!

Jellybeans, perhaps. Nothing leading edge.

Are you saying5 that TI doesn't have current mode regulators? Almost everything I've looked at in the last year is current mode.

I sure don't. I've never seen a behavioral that's good outside it's *NORMAL* operating conditions. That's never where the demons are.

They pay. Big time. Model? You're nuts.

All

frequency

Some

That's not the definition of single source :-)

I do use others, just not for really critical stuff like this where simulation is key.

Huh? That's not what I said. I said I am replacing a TI regulator that is not current-mode. It has to go because that one isn't up to the job. Of course they have developed better ones by now. But no behavioral models so one cannot simulate in a reasonable time frame.

Then you haven't tried hard enough with LTSpice :-)

By now they know me at LTC for lots of unorthodox uses.

Hah! Pay!!! LOL!!!

Good luck getting a chip maker to guarantee YOUR design no matter what you do.

Rick

All

frequency

our

Some

You only consider one source. That *is* a single source. Nuts!

With a behavioral, you can only simulate what the model builder anticipated. Again, that's rarely where the demons be. At least with full models, you have a chance.

Almost

Yet you will only use LTC because they're current mode.

Nonsense.

The models are useless outside their limited operational area. IOW, useless for guaranteeing operation.

You are an idiot.

You're batting 1000 today. Go back to your g5eometry lessons, with Bloggs.

It wasn't on trapezoidal integration, was it? :-o Sounds like the kind of gobbledeygook you get from funny simulation settings (or funny models that need more than default fudging!).

Tim

Yep. Last time I did that one single run too about four (!) hours.

Almost

You are not correctly reading what I write. I am using LTC because there are models that allow fast simulation. _Not_ because they are current mode. I only require that any switcher that replaces the old one is current mode.

confidence.

Sorry, but I have proven that statement wrong many times. For that to work you do need to establish good connections to their engineers though. I have.

Well, like with all unorthodox uses of such chips I want to get a blessing from their IC designers. Usually takes about a week, then they say yea or nay. Those guys know.

have

I've used entire mainframes for weeks on a single simulation. CPUs weren't as cheap, nor as powerful, as they are now. Not everyone had one sitting on their desk, either.

Almost

That's not what you said. You said it like current mode was something unique. It surely isn't.

confidence.

YOu *think* you've simulated everything that can go wrong. Obviously a model can't be used outside it's limits. Behaviorals have very limited useful area and they're rarely documented.

have

Well, I do not have a mainframe available here.

Almost

Where?

confidence.

The same goes for full models. There are limits to everything virtual. However, with behavioral models I've had years of successful designs. And yeah, I did discover the occasional model bug and also the occasional real bug on an IC. Where sim and real life did not jibe. Usually it meant that the datasheet didn't either. That's part of life.

anticipated.

have

You have about 100x the CPU power there.

reasons.

Almost

unique.

"Some don't have current-mode control and that's a no-no here."

Almost all do today. If you weren't making some point about it being somehow unique, it was a null statement.

confidence.

useless

Sure, but they're almost always more general than a behavioral. Most behaviorals don't even model their own supply current. Very few actually tell you *what* they're modeling.

I've had years of successful designs with little simulation at all.

Irrelevant. I'm not talking about bugs.

I'm waiting for Joerg to get to this point with you. You get to where you can't reply so you start insulting people. I don't get why you bother.

rick

Joerg has a brain and is a nice guy, unlike you, who are neither.

anticipated.

have

Probably even more. But that kind of power is no accessible to everyone. I am hoping that cloud deals arise some day where you can "rent" CPU time at more reasonable deals. That would really be useful to folks who have to run tough sims.

reasons.

Almost

unique.

^^^^

Makes no sense to discuss this point further.

confidence.

useless

model

area

LTC's usually do.

True. Although if you have a good relationship with a manufacturer's engineers they'll help you there. In my case this has enabled several unorthodox designs and they were, consequently, rewarded with increased business driven their way.

Our grandparents drove around without safety belts and survived :-)

If you know the limitations of the models I find them extremely useful. I do miss the good old bench time though, because nowadays there's a lot less of that than 20 years ago. I have relied on simulators my whole career but of course in the 80's the computers weren't up to snuff for the real heavy lifting.

You stopped a bit later than useful... ;^)

Uh, chances are that if your parents didn't have any children you won't either.

Rick

None I ever designed would care.

BTW, you can always make a sawtooth generator go faster by inserting a resistor in series with the cap. Basically it adds a step to the saw tooth, getting you to the limit faster.

Probably this one doesn't either, it's the simulator model that does. On this design I absolutely need a simulator model because of the ugly load. That shuts out most vendors.

Can't do that here. The chip has internal comparators and certain things need to happen at certain times on the ramp. So I'd rather keep that ramp linear.

Have you tried the op-amp trick to vary a fixed capacitor?

Depending on which way you need to shift it, lead of Lag will depend if you do a invert or non-inverting input.

This is done commonly using a LM324 in many circuits.,

Lead circuit +------------+ | | REf in | | + | |\| | REF out | +--+|-\ | ___ | | >-+---+----------+-|___|+---------+---------+ +----------+-|+/ | | /| | --- Lead Cap | +--------++ --- | | + + | | |\| | | + +--+|-\ + ___ | .-. | >+-++-|___|++ | |